What is an HRV and how does it work?
Heat Recovery Ventilation (HRV) systems are becoming increasingly common in cold climate construction and are almost indispensible in today’s super-insulated, airtight homes. As older homes are being retrofit and becoming tighter and more insulated, they are facing the same indoor air quality issues you find in new construction. HRVs are the best option in a cold climate to improve the indoor air quality of your home and conserve energy.
The main job of the HRV is to supply fresh outdoor air to the house while expelling stale indoor air—which contains things like moisture, animal dander and gases from combustion appliances and carpets. This is especially important in a home that is too tight to rely on passive air exchange. At the heart of the HRV is a heat exchanger (often called a core) that transfers heat from outgoing stale air to incoming fresh air without the airstreams mixing. Most HRVs recover between 70-90 percent of the heat, depending on the unit and controls, making them much more efficient than a standard exhaust fan that blows warm air directly outside.
The ducting of an HRV system typically supplies fresh air to bedrooms and living areas while exhausting humid air from bathrooms, kitchens, laundry rooms and crawlspaces. The HRV does not eliminate the need for a cooking fan, so a range hood should still be the main outlet for greases and smoke above the cook stove.
Balancing the HRV
The HRV is designed to be balanced, meaning it takes in as much air as it exhausts, maintaining close to neutral pressure inside the home. It should not create a negative pressure in the home, like an unregulated exhaust fan might, because that can cause appliances to backdraft (suck in air from an exhaust flue and bring dangerous combustion gases into the home). It’s also important to remember that HRVs are not meant to supply air to combustion appliances.
Energy Use & Maintenance
Residential-sized HRVs use about as much power as a 60-watt light bulb when running, and are getting more and more efficient. As with any appliance, an HRV requires some maintenance, such as checking the built-in filters every fall to see if they need to be cleaned or replaced.
Other Uses
You can install an in-line filter system on the warm-side supply air that will filter particles and odors from the incoming air. For example, in the winter this can help keep particulate pollution out of your home (from wood-burning and other sources). In the summer, this also helps protect you from forest fire or other air pollution.